This invention relates to an ultrasonic probe suitable for use in an ultrasonic diagnostic system, ultrasonic flaw detection system or the like.
An ultrasonic probe produces ultrasonic waves by a piezoelectric element and inspects the internal state of an object on the basis of reflected waves of the ultrasonic waves. Ultrasonic probes are used in a variety of application fields, for example, for diagnoses of the interiors of human bodies and detections of flaws in metal welds.
An ultrasonic beam emitted from a piezoelectric element has conventionally been focused using such means as an acoustic lens so that the resolution can be enhanced, which is called a focused beam method. The focused beam method can certainly provide a high resolution near the focal point. It is however accompanied by a drawback that the resolution is lowered as the point of an inspection or diagnosis moves away from the focal zone.
With a view toward solving the above drawback, ultrasonic probes driven by a synthetic aperture method have been studied. The synthetic aperture method is a method in which fan beams having a large beam width are emitted from a number of measurement points, and a number of pieces of information on the object collected from the measurement points, are synthesized to form a picture image of the object. According to the synthetic aperture method, the resolution is not governed by the distance but is determined by the beam width of each ultrasonic beam. The resolution is improved as the beam width becomes greater. Since a beam width is substantially in inverse proportion to the width of the aperture of the oscillating surface of a piezoelectric element, it is desirous to make the width of each aperture as small as possible. The resultant resolution becomes substantially the same level as the width of the aperture the oscillating surface of the piezoelectric element.
In the case of conventional ultrasonic probes, there was however a limitation to the sizes of piezoelectric elements suitable for use therein. If the width of a piezoelectric element is 5 mm or thinner, the piezoelectric element makes the fabrication of an ultrasonic probe very difficult.
In the case of an array-type ultrasonic probe which uses a plurality of piezoelectric elements, the piezoelectric elements can be obtained by slicing a single piece of piezoelectric element, and their intervals may thus be reduced to several hundred micrometers or so. Supposing that each piezoelectric material has a rectangular shape, one of its sides may hence be shortened to several hundred micrometers or so. However, a width of about 1-2 mm is necessary for connecting leads to the electrodes of a piezoelectric material. Therefore, it is impossible to shorten the length of the other side beyond the above limitation, leading to a limitation to the size of a piezoelectric element itself in its fabrication. Thus, it has been very difficult to reduce the width of the aperture of a piezoelectric element and to enlarge the beam width of an ultrasonic beam.
With the foregoing in view, the present invention has been completed. An object of this invention is to provide an ultrasonic probe which can produce ultrasonic beams having a great beam width.